Monday, March 18, 2013

What is "Haeckel's Tree of Life"?

The "Tree of LIfe" is an expression that you will find all over the web, usually referring to little more than a phylogenetic tree with only a few species in it, and certainly not all of Life, nor even the major groups of LIfe. More specifically, however, it seems commonly to refer to any tree that has Homo sapiens in it.

One tree that has intrigued me is found on Wikipedia's page called Tree of life (biology). It is labelled as "Haeckel's Stambaum der Primaten (1860s)", but in the text it is referred to as "the first sketch of the famous Haeckel's Tree of Life in the 1870s which shows 'Pithecanthropus alalus' as the ancestor of Homo sapiens."

The original JPEG file of the tree, dated 18 February 2009, has a compromise between these two contradictory statements: "The first sketch of the famous Heackel's Tree of Life which shows 'Pithecanthropus alalus' as the ancestor of Homo sapiens. Date: 1860s." No source is given for the picture.

Ernst Haeckel was the most famous popularizer of phylogenetic trees in the 19th century (he called them Stammbaum, literally "stem tree"). However, the illustration itself is not in the style of Haeckel's trees from the 1860s, which were drawn as realistic trees (see Who published the first phylogenetic tree?), nor is it in the style of his most famous tree from the 1870s, which is drawn as an oak tree (see Evolutionary trees: old wine in new bottles?). So, I decided to trace the history of this tree.

Haeckel published a slightly modified version of the sketch, with a different title, in:

It is worth noting that all of the names along the central axis are hypothetical, except for Homo sapiens. Pithecanthropus alalus, however, came to be associated with what is colloquially called Java Man, now named Homo erectus.

As far as I can determine, the hand-drawn version of the illustration (ie. the one in Wkipedia) first appeared in:

Gerhard Heberer was a German anthropologist and phylogeneticist, who studied Haeckel's work closely. He apparently passed a copy of the illustration to Herbert Wendt when the latter was expanding his book with many more illustrations. This book was a best-seller from the start, going through five German editions, before re-appearing in 1961 as Ich Suchte Adam: Die Entdeckung des Menschen [The Discovery of Humans], whence it went through another seven editions. It was translated into English, appearing in 1955 as I Looked for Adam, in 1956 as In Search of Adam: The Story of Man's Quest for the Truth About His Earliest Ancestors, and in 1972 as From Ape to Adam: Search for the Evolution of Man. It was also translated into several other languages (including Swedish in 1955 as I Urmänniskornas Spår: Förhistoriens Forskaräventyr).

The hand-drawn tree has appeared in print at least twice since its first appearance in Wendt's book. The most important of these is in:

Uwe Hoßfeld has told me: "I got the whole archive material from the Heberer family in 1990 and found the photo in his diaries." This explains the later history of the sketch, although not how Gerhard Heberer acquired the photo in the first place.

The date 1895 makes much more sense than do the 1860s and 1870s dates (as given in Wikipedia), especially given the publication date of the printed version.

The tree appears as Figure 1.4 on page 16 (in the chapter by Winfried Henke 'Historical overview of paleoanthropological research'), and is labelled: "First pedigree designed by Ernst Haeckel". As noted above, it is not the first pedigree from Haeckel, nor the first primate pedigree from him. Winfried Henke has told me that he got the sketch from Wendt's book.

As a final point, Haeckel's hand-drawn trees usually seem to match the published versions rather more closely than the one above does. For example, here is the hand-drawn original of his famous oak tree. Perhaps, the more stick-like tree was not treated as being a "real" picture.